Techniques to detect various objects using RFID tags are known. Related art is disclosed in Patent Literatures 1 and 2 and Non Patent Literatures 1 and 2, for example.
In Patent Literature 1, an RFID tag is placed at each of a plurality of article placement positions on a shelf, and an RFID reader reads a plurality of RFID tags to thereby detect the presence or absence of articles at the article placement positions. In Patent Literature 1, an article is placed between the RFID reader (antenna) and the RFID tag, and the article blocks the communication of signals, and thereby the presence or absence of the article is determined. Further, in Patent Literature 1, a limit (threshold) for determining the signal quality is set, and the presence or absence (I/O) of the article is detected by determining whether the signal is higher or lower than the threshold.
In Patent Literature 2, a plurality of RFID tags are on a plane facing a reader antenna, an envelope containing a metal piece is inserted between the reader antenna and the RFID tags, and the RFID reader reads the plurality of RFID tags to thereby detect the presence or absence or the position of the metal piece inside the envelope. In Patent Literature 2, like Patent Literature 1, the metal piece blocks the communication of signals, and thereby the presence or absence of the metal piece is determined, and the presence or absence (1/0) of the metal piece is detected by determining the success or failure of signal reading.
In Non Patent Literature 1, a tactile sensor where an RFID tag is attached to the side surface of a urethane grating and an antenna conductor is attached to the top and bottom surfaces of the urethane grating is used. Then, a plurality of tactile sensors are embedded in a knit-like artificial skin sheet, and the RFID reader reads the RFID tags to thereby detect the presence or absence or the position of contact with the artificial skin sheet. In Non Patent Literature 1, the presence or absence of contact is determined by pressing the tactile sensor from above and making a dent in the urethane, and thereby electrically connecting the antenna conductor and the RFID tag. Further, in Non Patent Literature 1, the presence or absence (I/O) of contact is detected by determining the presence or absence of a specified pressing force.
In Non Patent Literature 2, the RFID reader reads an RFID tag to thereby detect a temperature change according to a volume change in a dielectric layer near the RFID tag or a substance near the RFID tag, deformation of a beam near the RFID tag and the like.